Raman spectroscopy of basic copper(II) and some complex copper(II) sulfate minerals: Implications for hydrogen bonding

Abstract

Raman spectroscopy has been applied to the study of basic Cu sulfates including antlerite, brochiantite, posnjakite, langite, and wroewolfeite and selected complex Cu sulfate minerals. Published X-ray diffraction data were used to estimate possible hydrogen bond distances for the basic Cu sulfate minerals. A Libowitzky empirical expression was used to predict hydroxyl-stretching frequencies and agreement with the observed values was excellent. This type of study was then extended to complex basic Cu sulfates: cyanotrichite, devilline, glaucocerinite, serpierite, and ktenasite. The position of the hydroxyl-stretching vibration was used to estimate the hydrogen bond distances between the OH and the SO₄ units. The variation in bandwidth of the OH-stretching bands provided an estimate of the variation in these hydrogen bond distances. By plotting the hydrogen bond O…O distance as a function of the position of the SO₄ symmetric stretching vibration, the position of the SO₄ symmetric stretching band was found to be dependent upon the hydrogen bond distance for both the basic Cu sulfates and the complex Cu sulfates.